1. Field of the Invention
The present invention relates to a process for the purification of copper phthalocyanine pigments characterized by eliminating or substantially reducing equipment corrosion, material handling, safety and similar problems.
2. Prior Art
The introduction of phthalocyanine pigments in 1935 set new standards of excellence in the pigments consuming industries. They are characterized by their excellent light fastness, intensity, bleed and chemical resistance, extreme stability and exceptionally high tinting strength. Phthalocyanine pigments are restricted to the blue and green regions of the spectrum. Because of their excellent color values, working properties and low cost in addition to durability, the phthalocyanine blue and green pigments are used extensively.
The two processes most generally employed for producing copper phthalocyanine pigments are (1) heating phthalic anhydride, urea, a copper salt and a catalyst with or without a reaction medium such as chloronaphthalene or trichlorobenzene to 180.degree.-200.degree. C. and (2) heating phthalonitrile and a copper salt with or without a reaction medium or solid diluent. The product that results is generally a copper phthalocyanine blue pigment of about 65 to 70 percent purity. This is generally converted into a finely divided form by dry grinding. Such products are generally washed by methods well known to those skilled in the art. In general, the washing processes involve boiling the crude copper phthalocyanine blue in 10 percent of an acid, preferably HCl or H.sub.2 SO.sub.4, filtering and washing with hot water at about 85.degree. C. This results in a product that is about 95 percent pure which is a commercially pure product. This acid washing process has certain inherent disadvantages such as equipment corrosion, thus, problems of materials of construction, material handling and safety problems relevant to handling acid are presented.
______________________________________ Statement of the Relevant Patents U.S. Pat. No. Inventor Issue Date Assignee ______________________________________ 3,775,149 Langley et al 11/27/73 Ciba-Geigy 4,158,572 Blackburn et al 6/19/79 Ciba-Geigy ______________________________________
U.S. Pat. No. 3,775,149 discloses grinding an aqueous slurry of copper phthalocyanine in water which generates enough heat to raise the temperature to above 90.degree. C. However, there is no teaching of filtering at this temperature but rather the pigment may be subjected to a conventional treatment such as treatment with hydrochloric acid at elevated temperature followed by filtering.
U.S. Pat. No. 4,158,572 discloses a phthalocyanine pigment process which comprises dry grinding the crude phthalocyanine then stirring the product in an aqueous medium containing a surfactant, followed by isolating the pigmentary product. The second step, i.e., the stirring with a surfactant may be accomplished at a temperature from 70.degree. C. to the boil. Thus, a process of heating the slurry to a temperature of around 100.degree. C. is taught by this patent. However, there is no teaching or disclosure of filtering the material at this temperature but rather the prior art acid treatment is relied on for purification in most instances.